def two_sum(li, target):
for i in range(len(li)):
for j in range(i+1, len(li)):
if li[i] + li[j] == target:
return i, j
def bin_search(li, val, low, high):
while low <= high: # 候选区有值
mid = (low + high) // 2
if li[mid] == val:
return mid
elif li[mid] > val:
high = mid - 1
else: # li[mid] < val
low = mid + 1
return -1
def two_sum_2(li, target):
for i in range(len(li)):
a = li[i]
b = target - a
j = bin_search(li, b, i+1, len(li)-1)
if j > 0:
return i, j
def two_sum_4(li, target):
d = {}
for i, num in enumerate(li):
a = li[i]
b = target - a
if b in d:
return d[b], i
else:
d[a] = i
# [1,2,3,4]
